Organic dust exposure increases mast cell tryptase in bronchoalveolar lavage fluid and airway epithelium of heaves horses

Background Mast cell degranulation is believed to act as a key event in initiating and maintaining airway response to allergen challenge in human asthma. It is hypothesized that the mast cell may play a similar role in equine heaves, which shares many similarities with occupational dust-induced asthma. Objective The aim of this study was to quantify the mast cell proteinase tryptase in bronchoalveolar lavage fluid (BALF) from control and heaves-susceptible horses and to investigate tryptase mRNA and protein expression in pulmonary mast cells. Methods Equine BALF tryptase concentrations were determined by ELISA from control and heaves-susceptible horses pre and post 24 h hay/straw challenge (HSC). Tryptase mRNA and protein expression were investigated by quantitative PCR and immunohistochemistry in bronchial and bronchiolar tissue samples of control and heaves-susceptible horses. Results Both control and heaves-susceptible horses had significantly increased BALF tryptase concentrations following HSC (P=0.003 and 0.034, respectively). Increased numbers of tryptase-expressing intra-epithelial mast cells were demonstrated in heaves horses, but not controls, following challenge (P=0.02). Bronchiolar tissue from heaves horses removed from challenge contained significantly lower tryptase transcripts than that from control horses (P=0.02). Conclusion Mast cell degranulation and tryptase release into the airways occur following HSC of control and heaves-susceptible horses. The greater number of mast cells available in the bronchiolar epithelium of heaves horses may be clinically significant in the pulmonary inflammatory response of heaves.